sed截取nginx时间段日志 nginx截取变量字符串

题记：一般对字符串的操作有以下几种：求长度，截取字符串，拼接字符串，找字符串中某个字符的索引
1 expr 命令
1.1 定义
man 手册
Print the value of EXPRESSION to standard output. A blank line below separates increasing precedence
groups. EXPRESSION may be:
ARG1 | ARG2
ARG1 if it is neither null nor , otherwise ARG2
ARG1 & ARG2
ARG1 if neither argument is null or , otherwise
ARG1 < ARG2
ARG1 is less than ARG2
。。。等等
跟字符串相关的
match STRING REGEXP
same as STRING : REGEXP
substr STRING POS LENGTH
substring of STRING, POS counted from
index STRING CHARS
index in STRING where any CHARS is found, or
length STRING
length of STRING
1.2示例
[devtac@test_1 ~]$ expr length "how can i just let you walk away"
32
[devtac@test_1 ~]$ expr length "how "
4
[devtac@test_1 ~]$ expr substr "how can i just" 2 6
ow can
[devtac@test_1 ~]$ expr index "how can i how" h
1
# 常用linux 命令和相关问题解决